Rand et al. try to explore the way that in-group favoritism can change over time. Previous work on cooperation and evolutionary approaches to understanding cooperative behavior had suggested that in-group favoritism plays an important role in the development of cooperation. However, in a dynamic environment, it had been suggested that groups will need to respond to new conflicts and alliances and, one would expect, would have a more dynamic set of understandings of in-group favoritism.

Rand and his colleagues tested this through behavioral economic games/social dilemmas using democratic voters in Massachusetts in the run up to the 2008 election. Over a period of time in the year before the election, the researchers had democrats play a series of dictator games where each person was asked to divide $6 between themselves and a player who was identified as either being for Barrack Obama or Hilary Clinton. Indeed, they find an ingroup bias in that Obama supporters will give more money to other Obama supporters.

They found that after Clinton had conceded to Obama, Democrats were more generous toward supporter of their preferred candidate as compared to the competitor. This bias persisted up through the end of August until the Democratic National Convention in early September when it disappeared. The results show a strong gender effect in that the bias shown seems to only be present in men in the study, and not in woman. The authors suggest that this is a good real-world example of the dynamic nature of deep in-group favoritism biases and suggests that the ability to negotiate these biases reasonably quickly is (a) one reason that Obama won the election and (b) evidence of a more fundamental evolutionary trait.